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authorDaniel Baumann <daniel.baumann@progress-linux.org>2024-05-24 04:52:22 +0000
committerDaniel Baumann <daniel.baumann@progress-linux.org>2024-05-24 04:52:22 +0000
commit3d08cd331c1adcf0d917392f7e527b3f00511748 (patch)
tree312f0d1e1632f48862f044b8bb87e602dcffb5f9 /man3/flockfile.3
parentAdding debian version 6.7-2. (diff)
downloadmanpages-3d08cd331c1adcf0d917392f7e527b3f00511748.tar.xz
manpages-3d08cd331c1adcf0d917392f7e527b3f00511748.zip
Merging upstream version 6.8.
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
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-'\" t
-.\" Copyright (C) 2001 Andries Brouwer <aeb@cwi.nl>.
-.\"
-.\" SPDX-License-Identifier: Linux-man-pages-copyleft
-.\"
-.TH flockfile 3 2023-10-31 "Linux man-pages 6.7"
-.SH NAME
-flockfile, ftrylockfile, funlockfile \- lock FILE for stdio
-.SH LIBRARY
-Standard C library
-.RI ( libc ", " \-lc )
-.SH SYNOPSIS
-.nf
-.B #include <stdio.h>
-.P
-.BI "void flockfile(FILE *" filehandle );
-.BI "int ftrylockfile(FILE *" filehandle );
-.BI "void funlockfile(FILE *" filehandle );
-.fi
-.P
-.RS -4
-Feature Test Macro Requirements for glibc (see
-.BR feature_test_macros (7)):
-.RE
-.P
-All functions shown above:
-.nf
- /* Since glibc 2.24: */ _POSIX_C_SOURCE >= 199309L
- || /* glibc <= 2.23: */ _POSIX_C_SOURCE
- || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
-.fi
-.SH DESCRIPTION
-The stdio functions are thread-safe.
-This is achieved by assigning
-to each
-.I FILE
-object a lockcount and (if the lockcount is nonzero)
-an owning thread.
-For each library call, these functions wait until the
-.I FILE
-object
-is no longer locked by a different thread, then lock it, do the
-requested I/O, and unlock the object again.
-.P
-(Note: this locking has nothing to do with the file locking done
-by functions like
-.BR flock (2)
-and
-.BR lockf (3).)
-.P
-All this is invisible to the C-programmer, but there may be two
-reasons to wish for more detailed control.
-On the one hand, maybe
-a series of I/O actions by one thread belongs together, and should
-not be interrupted by the I/O of some other thread.
-On the other hand, maybe the locking overhead should be avoided
-for greater efficiency.
-.P
-To this end, a thread can explicitly lock the
-.I FILE
-object,
-then do its series of I/O actions, then unlock.
-This prevents
-other threads from coming in between.
-If the reason for doing
-this was to achieve greater efficiency, one does the I/O with
-the nonlocking versions of the stdio functions: with
-.BR getc_unlocked (3)
-and
-.BR putc_unlocked (3)
-instead of
-.BR getc (3)
-and
-.BR putc (3).
-.P
-The
-.BR flockfile ()
-function waits for
-.I *filehandle
-to be
-no longer locked by a different thread, then makes the
-current thread owner of
-.IR *filehandle ,
-and increments
-the lockcount.
-.P
-The
-.BR funlockfile ()
-function decrements the lock count.
-.P
-The
-.BR ftrylockfile ()
-function is a nonblocking version
-of
-.BR flockfile ().
-It does nothing in case some other thread
-owns
-.IR *filehandle ,
-and it obtains ownership and increments
-the lockcount otherwise.
-.SH RETURN VALUE
-The
-.BR ftrylockfile ()
-function returns zero for success
-(the lock was obtained), and nonzero for failure.
-.SH ERRORS
-None.
-.SH ATTRIBUTES
-For an explanation of the terms used in this section, see
-.BR attributes (7).
-.TS
-allbox;
-lbx lb lb
-l l l.
-Interface Attribute Value
-T{
-.na
-.nh
-.BR flockfile (),
-.BR ftrylockfile (),
-.BR funlockfile ()
-T} Thread safety MT-Safe
-.TE
-.SH STANDARDS
-POSIX.1-2008.
-.SH HISTORY
-POSIX.1-2001.
-.P
-These functions are available when
-.B _POSIX_THREAD_SAFE_FUNCTIONS
-is defined.
-.SH SEE ALSO
-.BR unlocked_stdio (3)